Method and apparatus for providing brightness control in an interferometric modulator (imod) display

ABSTRACT

Methods and systems for providing brightness control in an interferometric modulator (IMOD) display are provided. In one embodiment, an interferometric modulator display pixel is provided that includes a microelectromechanical systems (MEMS) interferometric modulator having an associated first color spectrum, and a color absorber located substantially in front of the interferometric modulator display pixel, in which the color absorber has an associated second color spectrum. The micro electromechanical systems (MEMS) interferometric modulator is operable to shift the first color spectrum relative to the second color spectrum to control a visual brightness of the interferometric modulator display pixel independent of a color of the interferometric modulator display pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/849,750, filed Aug. 3, 2010, entitled “METHOD AND APPARATUS FORPROVIDING BRIGHTNESS CONTROL IN AN INTERFEROMETRIC MODULATOR (IMOD)DISPLAY,” which is a continuation of U.S. patent application Ser. No.11/408,753, filed Apr. 21, 2006, now U.S. Pat. No. 8,004,743, entitled“METHOD AND APPARATUS FOR PROVIDING BRIGHTNESS CONTROL IN ANINTERFEROMETRIC MODULATOR (IMOD) DISPLAY,” and assigned to the assigneehereof. The entire disclosures of the prior applications are consideredpart of, and are incorporated by reference in, this disclosure.

TECHNICAL FIELD

The present invention relates generally to display devices, and moreparticularly to brightness control in interferometric modulator displaydevices.

BACKGROUND

Microelectromechanical systems (MEMS) include micromechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and/or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by atransparent medium (e.g., an air gap). As described herein in moredetail, the position of one plate in relation to the other plate canchange the optical interference of light incident on the interferometricmodulator. Such devices have a wide range of applications, and it wouldbe beneficial in the art to utilize and/or modify the characteristics ofthese types of devices so that their features can be exploited inimproving existing products and creating new products that have not yetbeen developed.

An interferometric modulator display device generally comprises multiplepixels, in which each pixel is operable to provide a range of visualcolors, for example, by changing the position of a corresponding plate(e.g., the metallic membrane) in relation to another plate (e.g., thestationary layer) to shift a color perceived by a user. Conventionalinterferometric modulator display devices, however, typically do nothave a brightness control (for each pixel) that is independent of pixelcolor-i.e., in conventional interferometric modulator display devicesthe brightness of a pixel is usually controlled by shifting a color ofthe pixel to an unperceivable color. Consequently, brightness control inconventional interferometric modulator displays is generally limited.

Accordingly, what is needed is an improved technique for providingbrightness control in an interferometric modulator display. The presentinvention addresses such a need.

SUMMARY

In general, in one aspect, this specification describes aninterferometric modulator display pixel that includes amicroelectromechanical systems (MEMS) interferometric modulator havingan associated first color spectrum, and a color absorber locatedsubstantially in front of the interferometric modulator display pixel,in which the color absorber has an associated second color spectrum. Themicroelectromechanical systems (MEMS) interferometric modulator isoperable to shift the first color spectrum relative to the second colorspectrum to control a visual brightness of the interferometric modulatordisplay pixel independent of a color of the interferometric modulatordisplay pixel.

Implementations may provide one or more of the following advantages. Aninterferometric modulator display is provided that implements brightnesscontrol (for each pixel) that is independent of a color associated witha pixel. Accordingly, an interferometric modulator display can provide agreater visual display of color gradations and shade in comparison toconventional interferometric modulator displays. In addition, the rangeof colors of such a display changes less with changes in spectrum of theambient illumination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A-5B illustrate one exemplary timing diagram for row and columnsignals that may be used to write a frame of display data to the 3×3interferometric modulator display of FIG. 2.

FIG. 6A is a cross section of an interferometric modulator of FIG. 1.FIGS. 6B-E are alternative embodiments of an interferometric modulator.

FIG. 7 illustrates a graph of an equilibrium equation for aninterferometric modulator.

FIG. 8 illustrates the simulated brightness of an interferometricmodulator using a green LED as the illumination source as a function ofthe air gap size.

FIG. 9 is a cross section of an interferometric modulator according toone embodiment of the invention.

FIGS. 10A-10C illustrate color spectra associated with aninterferometric modulator of FIG. 7.

FIG. 11 illustrates a flow diagram illustrating a process formanufacturing an interferometric modulator display according to oneembodiment.

FIGS. 12A-12I illustrate the process of manufacturing an interferometricmodulator display according to the process of FIG. 11.

FIG. 13 illustrates a cross section of an interferometric modulatoraccording to one embodiment of the invention.

FIGS. 14A-14B are system block diagrams illustrating an embodiment of avisual display device comprising a plurality of interferometricmodulators.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

As discussed above, conventional interferometric modulator displaydevices typically do not have a brightness control (for each pixel) thatis independent of pixel color. That is, in conventional interferometricmodulator display devices the brightness of a pixel is usuallycontrolled by shifting a color of the pixel to an unperceivable color.Thus, brightness control within conventional interferometric modulatordisplay devices is generally limited. Accordingly, this specificationdescribes an improved technique for providing brightness control in aninterferometric modulator display. In one embodiment, an interferometricmodulator display pixel is provided that includes amicroelectromechanical systems (MEMS) interferometric modulator havingan associated first color spectrum. The microelectromechanical systems(MEMS) interferometric modulator is operable to shift the first colorspectrum relative to a second color spectrum to control a visualbrightness of the interferometric modulator display pixel independent ofa color of the interferometric modulator display pixel.

Firstly, a description of an interferometric modulator displayembodiment will be described which has been conceived and reduced topractice by QUALCOMM Inc. This display operates effectively for itsstated purpose. However, it is always desirable to improve on theperformance thereof. To describe this modulator and its operation refernow to the following description in conjunction with the accompanyingfigures.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical gap with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thefixed partially reflective layer. Incident light that reflects from thetwo layers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack 16 are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the gap 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not shown) within the optical stack 16 may prevent shorting and controlthe separation distance between layers 14 and 16, as illustrated bypixel 12 b on the right in FIG. 1. The behavior is the same regardlessof the polarity of the applied potential difference. In this way,row/column actuation that can control the reflective vs. non-reflectivepixel states is analogous in many ways to that used in conventional LCDand other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in accordance with the embodimentof FIG. 1 in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single-chip or multi-chipmicroprocessor such as an ARM (Advanced RISC Machine), Pentium®, PentiumII®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051, a MIPS®, a PowerPC®, an ALPHA®, or any special purpose microprocessor such as a digitalsignal processor, microcontroller, or a programmable gate array. As isconventional in the art, the processor 21 may be configured to executeone or more software modules. In addition to executing an operatingsystem, the processor may be configured to execute one or more softwareapplications, including a web browser, a telephone application, an emailprogram, or any other software application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.”

For a display array having the hysteresis characteristics of FIG. 3, therow/column actuation protocol can be designed such that during rowstrobing, pixels in the strobed row that are to be actuated are exposedto a voltage difference of about 10 volts, and pixels that are to berelaxed are exposed to a voltage difference of close to zero volts.After the strobe, the pixels are exposed to a steady state voltagedifference of about 5 volts such that they remain in whatever state therow strobe put them in. After being written, each pixel sees a potentialdifference within the “stability window” of 3-7 volts in this example.This feature makes the pixel design illustrated in FIG. 1 stable underthe same applied voltage conditions in either an actuated or relaxedpre-existing state. Since each pixel of the interferometric modulator,whether in the actuated or relaxed state, is essentially a capacitorformed by the fixed and moving reflective layers, this stable state canbe held at a voltage within the hysteresis window with almost no powerdissipation. Essentially no current flows into the pixel if the appliedpotential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5A-5B illustrate one possible actuation protocol forcreating a display frame on the 3×3 array of FIG. 2. FIG. 4 illustratesa possible set of column and row voltage levels that may be used forpixels exhibiting the hysteresis curves of FIG. 3. In the embodimentshown in FIG. 4, actuating a pixel involves setting the appropriatecolumn to −V_(bias), and the appropriate row to +ΔV, which maycorrespond to −5 volts and +5 volts, respectively. Relaxing the pixel isaccomplished by setting the appropriate column to +V_(bias), and theappropriate row to the same +ΔV, producing a zero volt potentialdifference across the pixel. In those rows where the row voltage is heldat zero volts, the pixels are stable in whatever state they wereoriginally in, regardless of whether the column is at +V_(bias), or−V_(bias). As is also illustrated in FIG. 4, it will be appreciated thatvoltages of opposite polarity than those described above can be used,e.g., actuating a pixel can involve setting the appropriate column to+V_(bias), and the appropriate row to the same −ΔV. In this embodiment,releasing the pixel is accomplished by setting the appropriate column to−V_(bias), and the appropriate row to the same −ΔV, producing a zerovolt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the frame shown in FIG. 5A, pixels (1,1), (1,2), (2,2), (3,2) and(3,3) are actuated. To accomplish this, during a “line time” for row 1,columns 1 and 2 are set to −5 volts, and column 3 is set to +5 volts.This does not change the state of any pixels, because all the pixelsremain in the 3-7 volt stability window. Row 1 is then strobed with apulse that goes from 0, up to 5 volts, and back to zero. This actuatesthe (1,1) and (1,2) pixels and relaxes the (1,3) pixel. No other pixelsin the array are affected. To set row 2 as desired, column 2 is set to−5 volts, and columns 1 and 3 are set to +5 volts. The same strobeapplied to row 2 will then actuate pixel (2,2) and relax pixels (2,1)and (2,3). Again, no other pixels of the array are affected. Row 3 issimilarly set by setting columns 2 and 3 to −5 volts, and column 1 to +5volts. The row 3 strobe sets the row 3 pixels as shown in FIG. 5A. Afterwriting the frame, the row potentials are zero, and the columnpotentials can remain at either +5 or −5 volts, and the display is thenstable in the arrangement of FIG. 5A. It will be appreciated that thesame procedure can be employed for arrays of dozens or hundreds of rowsand columns. It will also be appreciated that the timing, sequence, andlevels of voltages used to perform row and column actuation can bevaried widely within the general principles outlined above, and theabove example is exemplary only, and any actuation voltage method can beused with the systems and methods described herein.

FIG. 6A is a cross section of the embodiment of FIG. 1, where a strip ofmetal material 14 is deposited on orthogonally extending supports 18. InFIG. 6B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 6C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are referred to herein as support posts. Theembodiment illustrated in FIG. 6D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the gap, as in FIGS. 6A-6C, but the deformable layer 34does not form the support posts by filling holes between the deformablelayer 34 and the optical stack 16. Rather, the support posts are formedof a planarization material, which is used to form support post plugs42. The embodiment illustrated in FIG. 6E is based on the embodimentshown in FIG. 6D, but may also be adapted to work with any of theembodiments illustrated in FIGS. 6A-6C as well as additional embodimentsnot shown. In the embodiment shown in FIG. 6E, an extra layer of metalor other conductive material has been used to form a bus structure 44.This allows signal routing along the back of the interferometricmodulators, eliminating a number of electrodes that may otherwise havehad to be formed on the substrate 20.

In the above-identified modulators of FIG. 1, there are two states foroperation of the device: relaxed and activated. When the device isactuated snap-in has occurred, that is, the moveable membrane has movedinto engagement based upon the “hysteresis window”. In one embodiment, amodulator in accordance with the present invention avoids thisinstability to provide stable control of the brightness using theapplied voltage. To describe this feature in more detail, refer now tothe following description in conjunction with the accompanying figures.

At equilibrium, the electrostatic and mechanical spring forces will beequal:

F_(mechanical) = F_(electrostatic)${k \cdot x} = \frac{ɛ_{0} \cdot A \cdot V^{2}}{2 \cdot \left( {\frac{x_{dielectric}}{ɛ_{dielectric}} + x_{air} - x} \right)^{2}}$

where A is the area of the pixel, and ε₀ is the permittivity of space,ε_(dielectric) is the relative dielectric constant of the dielectricmaterial, k is the spring constant, V is the applied voltage, andx_(air) is the maximum thickness of the air gap.

A graph of this equilibrium equation is shown in FIG. 7. As is seen inthis figure, there are two places where the slope of x becomes infinite.Finding the snap-in instability point using V as the independentvariable is mathematically difficult. It is easier to consider V as adependent function of x, then setting the derivative of dV/dx equal tozero:

$0 = {\frac{V}{x} = {\frac{}{x}\sqrt{\frac{2 \cdot k \cdot \left( {\frac{x_{dielectric}}{ɛ_{dielectric}} + x_{air} - x} \right)^{2}}{ɛ_{0} \cdot A}}}}$

After differentiation and a little simplification, this becomes:

$x = \frac{\frac{x_{dielectric}}{ɛ_{dielectric}} + x_{air}}{3}$

Accordingly, it has been found that approximately for ⅓ of the totaldistance between the two electrodes, the members can be controlled. Theimportant point is that the control voltage may extend from 0 eitherpositive or negative for small excursions, as long as the point ofinstability is not exceeded. If the voltage exceeds the instabilityvoltage, then the moveable membrane will snap down to the dielectric,and there will no longer be a one-to-one correspondence between appliedvoltage and the membrane position (at least until the voltage is broughtclose to zero again).

FIG. 8 illustrates the simulated brightness of an interferometricmodulator using a green LED as the illumination source as a function ofthe air gap size in accordance with one embodiment of the invention.

Assuming the spring for this interferometric modulator is arranged soits force is zero at a gap of 540 nm, the point of instability is at 540nm*(1⅓)=360 nm. Since the maximum brightness is at 440 nm, thisinterferometric modulator may be controlled in an analog fashion fromminimum brightness (at 540 nm) to maximum brightness (at 440 nm) withoutconcern for the snap-in instability point.

FIG. 9 illustrates a cross-section of an interferometric modulator 700in accordance with one embodiment of the present invention. Theinterferometric modulator 700 includes a substrate 702, an optical stack704, a mechanical layer 706, and support posts 708 to support themechanical layer 706. In one embodiment, the substrate 702 issubstantially transparent and/or translucent. For example, the substrate702 can be glass, silica, and/or alumina. In one embodiment, the opticalstack 704 comprises several fused layers, including an electrode layer(e.g., indium tin oxide (ITO)), a partially reflective layer (e.g.,chromium), and a transparent dielectric. The partially reflective layercan be formed from a variety of materials that are partially reflectivesuch as various metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials. In one embodiment, the interferometric modulator 700further includes an oxide layer 710 to electrically isolate themechanical layer 706 from the optical stack 704 when the mechanicallayer 706 is activated.

The interferometric modulator 700 also includes a color absorber 712,for example, to provide for brightness control. In general, the colorabsorber 712 substantially absorbs light except light at a peak color,or absorbs light except light within a pre-determined range ofwavelengths. For example, referring to FIG. 10A, the color absorber 712can have an associated color spectrum 804 with a peak color of green(e.g., a color at a wavelength substantially near 520 nm) as shown ingraph 800A. Also, the interferometric modulator 700, at some positionhas an associated (reflectance) color spectrum that reflects light at agiven peak wavelength.

For example, as shown in graph 800A, the interferometric modulator 700in a relaxed position (ignoring the effect of the absorber 712), has apeak reflectance color of red (e.g., a color at a wavelengthsubstantially near 700 nm). An associated color spectrum 806 centered atapproximately 700 nm is illustrated. A visual brightness of colorassociated with the interferometric modulator 700 is a result of thecombination of the color spectrum 804 (associated with the colorabsorber 712) and the color spectrum 806 (from the interferometricmodulator 700 in a relaxed position and ignoring the effect of theabsorber upon the interferometric modulator) as shown in graph 800B ofFIG. 10A. In one embodiment, the final color, represented by colorspectrum 808, is the product of the inteferometric modulator reflectancespectrum and the square of the absorber transmittance spectrum, sincethe light has to pass through the absorber twice. As the mechanicallayer 706 moves closer to the optical stack 704 (through the gap 714),the light reflectance properties of the interferometric modulatorchanges, and accordingly, the (reflectance) color spectrum associatedwith the interferometric modulator 700 shifts.

Referring to the example graphs of 802A and 804A of FIGS. 10B and 10C,respectively, as the mechanical layer 706 moves closer to the opticalstack 704, the color spectrum associated with the interferometricmodulator 700 (ignoring for the purposes of this example the effect ofthe absorber 712) increasingly overlaps with the color spectrum 804associated with the color absorber 712. The visual brightness of colorassociated with the interferometric modulator increases with greateroverlap between the color spectrum associated with the interferometricmodulator 700 and the color spectrum associated with the color absorber712 (as shown by graphs 800B, 802B and 804B). In graph 802A, themechanical layer 706 has moved closer to the dielectric layer 710 andnarrowed the gap 714, resulting in a reflected color spectrum 810. Theproduct of the color spectrum 810 with the square of color spectrum 804results in a color spectrum 812 in graph 802B. Color spectrum 812 coversa greater area than color spectrum 808 and is therefore brighter.Similarly, in graph 804A, the mechanical layer 706 has moved even closerto the dielectric layer 710, resulting in a reflected color spectrum814. The product of the color spectrum 814 with the square of the colorspectrum 804 results in a color spectrum 816 in graph 804B. The colorspectrum 816 covers a greater area than the color spectrum 812 and istherefore brighter. In like manner, the visual brightness of colorassociated with the interferometric modulator decreases with lessoverlap between the color spectrum associated with the interferometricmodulator 700 and the color spectrum associated with the color absorber712. Thus, unlike conventional interferometric modulators, a visualbrightness of the interferometric modulator can be controlled withouthaving to shift a color of the interferometric modulator to anunperceivable color. In one embodiment, interferometric modulator 700can be activated as described above in connection with FIG. 3.Alternatively, the interferometric modulator 700 can be fully controlledin an analog manner as described in co-pending U.S. patent applicationentitled “Analog Interferometric Modulator Device”, application Ser. No.11/144,546, which is incorporated herein by reference in its entirety.

Continuously variable control can be provided in a variety of ways. Forexample, referring again to FIG. 9, one way is to size the gap 714 suchthat a desired color spectrum results from movement of the mechanicallayer 706 through less than the ⅓ snap-through point to the oxide layer710. Another example is to use a switch to pinch off the voltage beforethe interferometric modulator has gone to its new state, the amount ofvoltage, or charge, being enough to close the gap 714 a desired amount,also without exceeding the snap-through point to the oxide layer 710.Another example is to put the reference electrode behind the moveablemembrane (instead of using a transparent conductor like ITO). Thisallows a broader range of gaps before the snap-through at ⅓ of the gap.

FIG. 11 illustrates a process 900 of fabricating an interferometricmodulator (e.g., interferometric modulator 700) in accordance with oneembodiment. Referring to FIG. 11, the process 900 begins with providinga substrate (step 902). Referring to the example of FIG. 12A, asubstrate 1002 is provided. In one embodiment, the substrate 1002 issubstantially transparent and/or translucent. In one embodiment, thesubstrate 1002 comprises glass. A color absorber is deposited (step904). As shown in FIG. 12B, a color absorber 1004 is deposited over thesubstrate 1002. The color absorber 1002 can be a thin film thatsubstantially absorbs light for a pre-determined range of wavelengths. Aconductive layer is formed (step 906). As shown in FIG. 12C, aconductive layer 1006 is formed over the color absorber 1004. In oneembodiment the conductive layer 1006 comprises one or more layers and/orfilms. For example, in one embodiment the conductive layer 1006comprises a conductive layer (e.g., indium tin oxide (ITO)) and apartially reflective layer (e.g., chromium). An oxide layer is deposited(step 908). As shown in FIG. 12D, an oxide layer 1008 is deposited overthe conductive layer 1006. In one embodiment, the oxide layer 1008comprises a silicon oxide compound (Si_(x)O_(y)). A sacrificial layer isdeposited (step 910). Referring to FIG. 12E, a sacrificial layer 1010 isdeposited over the oxide layer 1008. In one embodiment, the sacrificiallayer 1010 comprises molybdenum. In one embodiment, the height of thesacrificial layer 1010 determines the amount of spacing between theconductive layer 1006 (or conductive plate) and a second conductiveplate (e.g., a mechanical layer discussed below).

After deposition of the sacrificial layer, the process of forming thesupport posts for the mechanical layer begins. Accordingly, thesacrificial layer is etched (step 912). Referring to the example of FIG.12F, the sacrificial layer 1010 is etched at locations where supportposts are desired. In addition, one or more layers below the sacrificiallayer 1010 can be etched as well. A plurality of posts is formed (step914). As shown by FIG. 12G, posts 1012 are formed within the etchedportions of the layers of the interferometric modulator. In oneembodiment, the posts 1012 are formed using a planarization techniquefollowed by photolithography to remove unwanted portions of the materialthat comprise the posts 1012. The posts 1012 can comprise a polymer. Amechanical layer is formed (step 916). Referring to the example of FIG.12H, a mechanical layer 1014 is formed over the sacrificial layer 1010and the posts 1012. In one embodiment, the mechanical layer 1014comprises a movable reflective layer as discussed above. In oneembodiment, the mechanical layer 1014 comprises aluminum/nickel. Thesacrificial layer is released (step 918). Referring to FIG. 12I, thesacrificial layer 1010 is released to form an air gap 1016 between themechanical layer 1014 and the oxide layer 1008. The sacrificial layer1010 can be released through one or more etch holes formed through themechanical layer 1014.

FIG. 13 illustrates a cross-section of an interferometric modulator 1200in accordance with one embodiment of the invention. In the embodimentshown in FIG. 13, the color absorber 1004 is deposited on a surface ofthe substrate 1002 opposite from conductive layer 1006. Theinterferometric modulator 1200 further includes one or more (colored)light sources 1202 and one or more mirrors 1204 (e.g., half-silveredmirrors) to provide a color spectrum for brightness control. Thetechniques for brightness control are similar to techniques discussedabove. The light sources 1202 can be a narrow spectrum light source(e.g., a laser or LED) or a broad spectrum light (e.g., a white lampsuch as a high pressure mercury lamp or a carbon arc lamp). The colorabsorber 1004 can be a separate device such as a color wheel. In anembodiment in which multiple light sources are implemented, one lightsource can be used to illuminate only ⅓ of the pixels of aninterferometric modulator display, and the other light sources could beused to illuminate the remaining pixels of the interferometric modulatordisplay. Alternatively, one light source could be used to illuminate allof the pixels of an interferometric modulator display at one time, andthen during another period of time, a second light source could be usedto illuminate all of the pixels of an interferometric modulator displayat one time, e.g., in accordance with conventional field sequentialcolor techniques. The embodiment illustrated in FIG. 13 may be used, forexample, in a projection display system.

FIGS. 14A and 14B are system block diagrams illustrating an embodimentof a display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays as described herein. In other embodiments, the display 30includes a flat-panel display, such as plasma, EL, OLED, SIN LCD, or TFTLCD as described above, or a non-flat-panel display, such as a CRT orother tube device, as is well known to those of skill in the art.However, for purposes of describing the present embodiment, the display30 includes an interferometric modulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 14B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the invention is intended to avoid the problemscreated by using a bi-stable display and bi-stable display driver. Inone embodiment, the driver controller 29, array driver 22, and displayarray 30 are appropriate for any of the types of displays describedherein. For example, in one embodiment, driver controller 29 is aconventional display controller (e.g., an interferometric modulatorcontroller). In another embodiment, array driver 22 is a conventionaldriver (e.g., an interferometric modulator display driver). In oneembodiment, a driver controller 29 is integrated with the array driver22. Such an embodiment is common in highly integrated systems such ascellular phones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array (e.g., a displayincluding an array of interferometric modulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure-or heat-sensitive membrane.In one embodiment, the microphone 46 is an input device for theexemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some embodiments control programmability resides, as described above,in a driver controller which can be located in several places in theelectronic display system. In some cases control programmability residesin the array driver 22. Those of skill in the art will recognize thatthe above-described optimization may be implemented in any number ofhardware and/or software components and in various configurations.

Various embodiments of an interferometric modulator display have beendescribed. Nevertheless, one or ordinary skill in the art will readilyrecognize that various modifications may be made to the implementations,and any variation would be within the spirit and scope of the presentinvention. For example, process steps discussed above in connection withFIG. 11 may be performed in a different order and still achievedesirable results. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit can scope ofthe following claims.

What is claimed is:
 1. A display pixel comprising: a reflective displayelement having an associated first color spectrum associated with afirst color; a color filter having an associated second color spectrumassociated with a second color that is different than the first color;wherein the display element is operable to tune the first color spectrumrelative to the second color spectrum to provide multiple levels ofbrightness of the second color.
 2. The display pixel of claim 1, whereinthe display pixel is configured to display at least part of an image byreflecting incident ambient light.
 3. The display pixel of claim 1,wherein the display element includes an interferometric modulator. 4.The display pixel of claim 1, wherein the color filter includes a colorabsorber located substantially in front of the display element, thecolor absorber having the second color spectrum.
 5. The display pixel ofclaim 1, wherein the first color spectrum has a first peak wavelengthand the second color spectrum has a second peak wavelength, and whereinthe display element shifts the first peak wavelength relative to thesecond peak wavelength to provide the multiple levels of brightness ofthe second color.
 6. The display pixel of claim 1, wherein the visualbrightness of the display pixel increases with greater overlap betweenthe first color spectrum and the second color spectrum, and decreaseswith less overlap between the first color spectrum and the second colorspectrum.
 7. The display pixel of claim 1, further comprising one ormore light sources to provide light to the color filter.
 8. The displaypixel of claim 7, wherein a combination of the one or more light sourcesand the color filter provides light at the second color spectrum.
 9. Thedisplay pixel of claim 7, wherein the one or more light sources includesat least one of a laser, a light-emitting diode (LED), a high pressuremercury lamp, and a carbon arc lamp.
 10. The display pixel of claim 1,wherein the display element includes a reflective surface movablebetween a first position and a second position to tune the first colorspectrum relative to the second color spectrum.
 11. The display pixel ofclaim 1, wherein the brightness is a visual brightness.
 12. A displaycomprising the display pixel of claim 1, the display further comprising:a processor that is in electrical communication with the display pixel,the processor being configured to process image data; and a memorydevice in electrical communication with the processor.
 13. The displayof claim 12, further comprising: a first controller configured to sendat least one signal to the display pixel; and a second controllerconfigured to send at least a portion of the image data to the firstcontroller.
 14. The display of claim 12, further comprising an imagesource module configured to send the image data to the processor. 15.The display of claim 14, wherein the image source module includes atleast one of a receiver, transceiver, and transmitter.
 16. The displayof claim 12, further comprising an input device configured to receiveinput data and to communicate the input data to the processor.
 17. Adisplay pixel comprising: means for reflecting light having anassociated first color spectrum associated with a first color; and meansfor filtering light having an associated second color spectrumassociated with a second color that is different than the first color;wherein the reflecting means is operable to tune the first colorspectrum relative to the second color spectrum to provide multiplelevels of brightness of the second color.
 18. The display pixel of claim17, wherein the reflecting means includes an interferometric modulatorconfigured to display at least part of an image by reflecting incidentambient light.
 19. The display pixel of claim 17, wherein the reflectingmeans includes a reflective surface movable between a first position anda second position to tune the first color spectrum relative to thesecond color spectrum.
 20. The display pixel of claim 17, wherein thefiltering means includes a color absorber located substantially in frontof the reflecting means, the color absorber having the second colorspectrum.
 21. The display pixel of claim 17, further comprising one ormore light sources to provide light to the filtering means.
 22. Thedisplay pixel of claim 21, wherein a combination of the one or morelight sources and the filtering means provides light at the second colorspectrum.
 23. The display pixel of claim 17, wherein the brightness is avisual brightness.
 24. A method of making a display pixel, the methodcomprising: forming a reflective display element having an associatedfirst color spectrum associated with a first color; and providing acolor filter having an associated second color spectrum associated witha second color that is different than the first color; wherein thedisplay element is operable to tune the first color spectrum relative tothe second color spectrum to provide multiple levels of brightness ofthe second color.
 25. The method of claim 24, wherein forming a displayelement includes forming on an interferometric modulator configured todisplay at least part of an image by reflecting incident ambient light26. The method of claim 24, wherein providing a color filter includesforming a color absorber substantially in front of the display element.27. The method of claim 24, wherein forming a display element includes:forming a reflective surface movable between a first position and asecond position to tune the first color spectrum relative to the secondcolor spectrum.
 28. The method of claim 24, further comprising:providing one or more light sources to provide light to the colorfilter, wherein a combination of the one or more light sources and thecolor filter provides light at the second color spectrum.